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The Fundamentals of Metal Cutting

Perhaps the most common procedure done in a stamping die is cutting. In this process, metal is cut off by placing it in the small gap between the two bypassing tool steel sections. This gap is also known as the cutting clearance. The metal cutting process does not only require a great amount of force, but it creates a great deal of shock as well. That is why metal cutting is among the most severe stamping operations. Too much shock can result to die sections that break, punches that snap and presses that fail.

Imagine the situation wherein you are holding a hammer and were told to set it on a nail, then put it into a piece of wood; you are not likely to achieve anything. However, if you were instructed to raise the hammer then strike the nail, it would surely go into the piece of wood with not much effort. The power of the hammer as it falls, together with the shock, carries out the required work.

If ever you have been in a stamping plant where thick, high-strength steel is being cut, you could literally feel the floor vibrate each time the press cycled. Presses that are designed for cutting high-strength or heavy materials often come with additional heavy-duty frames plus components that can endure incredible shock. Some presses are incorporated with special dampening units to help absorb and dissipate the shock.

What Occurs During Metal Cutting?

As a start, you have to be aware that at times, you have to change the way you see sheet metal. In spite of its physical appearance, strength, weight and density, it is an elastomer. This means that, when it is exposed to a great amount of force, it behaves just like rubbery plastic. It is comparable to Silly Putty, the rubbery stuff inside a red egg, which you may have played with during your childhood. There are metals that are a lot more rubbery than others. On the other hand, high-strength steel and other harder metal are far from what Silly Putty looks like.

In many cutting processes, the metal is stressed until it fails between two components or bypassing die sections. In order for metal to be cut, the die needs a cutting punch, as well as mating section to which the punch goes through. The cutting clearance or distance between cutting sections differs as regards to the type of metal, hardness, thickness and desired edge quality.

Too much or too little clearance between cutting sections can create excessive burr on the part. To reduce the burr height, there must be a sufficient cutting clearance between the cutting sections, and these should be ground from time to time to keep a perfectly square edge. The process of grinding die sections is simply called “sharpening the section” by diemakers and technicians.

Once the mating and punch sections have been ground, they have to be regularly shimmed back up to their operational height. Shimming refers to the process through which thin sheets of stainless steel or other material are placed below the ground section to compensate for what has been ground off. Grinding and shimming are the common tasks performed in a basic maintenance procedure.

What is a Stamping Die?

A stamping die is a unique precision tool, which is used to cut metal sheet and form it into a particular shape. Dies contain cutting and forming sections that are usually made from special hardenable steel, known as tool steel. These cutting and forming sections can also be made from different hard wear-resistant materials, like carbide.

Stamping is a cold-forming process, in which heat is neither used on purpose into the die nor the sheet. However, since the cutting and forming process entails friction, which in turn generates heat, stamped parts that leave the dies are often very hot. Dies used in making microelectronics are available in a variety of sizes, some small enough to fit your palm, while others can reach 20 square ft by 10-ft. thickness and can, therefore, be used in making the sides of an automobile body.

Types of Dies

There are different types of stamping dies, and all perform any of the two basic operations of cutting, forming or both. There are robotically-loaded line dies, manually-loaded line dies, fully-automated progressive dies and fully-automated transfer dies.

Cutting

The operation most commonly done in a stamping die is cutting. To cut off the metal, it is placed between 2 bypass tool steel sections with a small gap in between them, which is also referred to as the cutting clearance.

Cutting clearance can vary, depending on the type of cutting operation done, properties of metal and the preferred edge condition of the part. Usually, the cutting clearance is expressed in terms of metal thickness percentage. The cutting clearance most commonly used is approximately 10% of the metal’s thickness.

There are several different cutting operations that come with their own distinct function. The most common are as follows:

Trimming

The external perimeter of the flat sheet metal is cut off to give the desired shape to the piece part. The excess is usually discarded as scrap.

Notching

Notching, which is often associated with progressive dies, is a process wherein cutting is done progressively on the outer part of a sheet metal strip to produce a given strip profile.

Blanking

Blanking is a double-purpose cutting operation often done on a larger scale. It is used in operations where the slug is kept for more pressworking. At times, it is used to sever finished piece parts detached from the sheet metal. The shaped sheet metal slug taken out from the sheet through this process is known as the blank, a piece of sheet metal that can be later cut or formed.

Piercing

Piercing, also called perforating, is an operation wherein metal is cut to produce a round, square or specially-shaped hole in a formed part or flat sheet metal. Piercing is different from blanking mainly because the slug is removed as scrap in piercing, while the slug is used in blanking. The cutting punch that creates the hole is known as the pierce punch and the hole is called the matrix.

Lancing

Lancing is the process of slicing or slitting the metal to free up metal, but not separate it from the strip. Lancing is usually performed in progressive dies to produce a part carrier known as a flex or stretch web.

Shearing

Since shearing cuts or slices the metal along a straight line, this method is commonly used for creating square and rectangular blanks.